1. Field of the Invention
The invention relates in general to a method of cleaning and maintenance used for a rotational etching tool, and more particularly to a method combining a PM (preventive maintenance) computer program to clean the rotational etching tool automatically and rapidly.
2. Description of the Related Art
The machines of manufacturing the semiconductors, in the form of so-called wafer (disk-shaped article based on silicon) require preventive maintenance (PM). For example, the maintenance of rotational etching tool, for treating one wafer in each case with at least two media and with a carrier to hold the wafer, has been performed with the hands by ejecting deionized (DI) water from a DI gun. However, the steps of PM, such as mechanical disassembly before DI water ejection, are usually complicated and time-consuming.
Recently, the most commercial successful rotational etching tools are provided by SEZ Semiconductor-Equipment Zubehor furdie Habbleiterfertigung (Villach, AT). The related mechanical structure and function in details have been disclosed in U.S. patents, such as U.S. Pat. No. 4,903,717, U.S. Pat. No. 6,536,454 and U.S. Pat. No. 6,383,331. The etching may be of a dry type (etched by gases) or wet type (etched by chemical liquids). FIG. 1 illustrates a sectional view of a rotational etching tool. There are several etching chambers, a cleaning chamber 104, and a wafer supporting means such as chuck 112 in the process room 102. Those etching chambers situated below the cleaning chamber 104 are the first etching chamber 106, the second etching chamber 108 and the third etching chamber 109 (from the top down). The chuck 112 is used for holding the wafer 116 by the lateral guiding elements (often also called pins) 114, projected from the top surface 112a of the chuck 112. The lateral guiding elements 114 are guided excentrically and grip the wafer 116 along its periphery in the operational position. The wafer 116 is held aligned parallel to the top surface 112a of the chuck 112. Here holding wafer can be done using a vacuum or the wafer 116 floats on an air cushion and is prevented from sliding off sideways by lateral guiding elements 114. The lack of physical contact between the rest of the wafer 116 with the top surface 112a of the chuck 112 helps to prevent damage to the wafer during treatment.
The chuck 112 may further has a gas supply channel (not shown). A gas, supplied through the channel and existing between the wafer 116 and chuck 112, is jetted against the guiding elements 114 and the adjacent portion of the lower surface of the wafer 116. In this way, the passage of etching fluid to the underside of the wafer 116 can be prevented, especially the undesirable etched potions in the region of the guiding elements 114 (so-called pin mark). Also, the chuck 112 is connected to a shaft 118 within an elevated part 120, so that the chuck 112 can be rotated on the shaft 118, and moved back and forth between the cleaning chamber 104 and the etching chambers (106, 108 and 109) in the direction of the arrow F.
In wet-etching process, the treatment liquid (such as etching liquid and rinse water) and gas (such as N2 and isopropyl alcohol (IPA)) are stored in the liquid tanks and gas tanks, respectively. The treatment fluid (liquid and gas) can be transported via the medium conduit to the conduit terminate, such as medium nozzle. The medium nozzles positioned at a distance from the wafer will discharge the media according to the stage requirement of etching process. Also, each etching chamber is connected to the associated etching liquid tank via a conduit, for recycle of etching liquid. The cleaning chamber is connected to a discharge conduit to drain the deionized water after rinse.
As shown in FIG. 1, the first etching liquid 136, the second etching liquid 138 and the third etching liquid 139 are stored in the first etching liquid tank 126, the second etching liquid tank 128 and the third etching liquid tank 129, respectively; also, are transported via the first conduit 146, the second conduit 148 and the third conduit 149 to the first medium nozzle 156, the second medium nozzle 158 and third medium nozzle 159, respectively. Preferably, those medium nozzles (156, 158 and 159) are positioned in a joint aperture, such as a medium dispenser 160, to maintain the relative distance between the chuck 112 and nozzles. The DI water nozzle and N2 nozzle are also positioned above the wafer 116 to eject DI water and N2 as required. Furthermore, the first etching chamber 106, the second etching chamber 108 and the third etching chamber 109 are connected to the first etching liquid tank 126, the second etching liquid tank 128 and the third etching liquid tank 129, respectively. Each conduit leads to a three-way valve (not shown). By appropriate setting the valves, etching liquid withdrawn from the etching chamber can either be recycled into the etching liquid tank, or drained through the discharge conduit.
General steps of wet-etching process are described as follows:
(a) Wafer 116 over the chuck 112 is rotated around its axis at a certain speed, and the surface of the wafer 116 is then wetted with a liquid, for example, deionized water.
(b) The chuck 112 is moved to the position associated with the appropriate etching chamber. For example, the chuck 112 is moved downward to the first etching chamber 106 if the first etching liquid 126 is required to use. Then, the etching liquid is applied to the wetted surface of the wafer 116.
(c) The surface of the wafer 116 is washed with a non-etching liquid (such as deionized water), and dried with a volatile gas (such as N2).
The etching liquid comprises at least one of following acids: hydrofluoric acid, nitric acid, phosphoric acid and sulfuric acid. In semiconductor manufacturing, it is known that a silicon dioxide layer can be etched with aqueous hydrofluoric acid, water-soluble hexafluorosilicic acid (H2SiF6) being formed. Addition of ammonium fluoride to hydrofluoric acid is also known, and this etching liquid is so-called as xe2x80x9cBHFxe2x80x9d (buffered hydrogen fluoride) or xe2x80x9cBOExe2x80x9d (buffered oxide etch). After the etching process is conducted for several times, it is required to do the cleaning and maintenance job for the interior of etching tool, especially xe2x80x9cBOExe2x80x9d being applied as one of etching liquids. When BOE is applied to the surface of the spinning wafer 116, it is thrown off and adheres to the walls of the etching chamber, and turns into the form of crystal-powder after drying. Those BOE powders (numeral 170) accumulated in etching chamber will contaminate the wafer; thus, it requires a regular cleaning and maintenance to remove those BOE powders.
FIG. 2 is a block diagram of a conventional PM (Preventive Maintenance) process for rotational etching tool. The conventional PM process comprises the steps of:
(1) Preparation for maintenancexe2x80x94the maintenance crew need to wear chemical splash goggles, a chemical resistant apron or garment, and chemical resistant gloves; also, cleanroom wipers, cotton wraps and IPA (isopropyl alcohol) should be ready to use.
(2) Disassembly of etching tool hardwarexe2x80x94the medium dispenser 160 is detached first, and then the chuck 112 is removed from the process room 102.
(3) Clean and wipexe2x80x94the walls and edges of etching chambers are cleaned by DI water using DI gun (held by man), and then dried by cleanroom wipers.
(4) Reassembly of etching tool hardware and testxe2x80x94the chuck 112 and the medium dispenser 160 are put back, and then the chuck movement is checked to make sure it works well.
(5) Wipe with IPAxe2x80x94the chuck 112, the medium dispenser 160 and the accessory around are wiped with IPA.
(6) flush conduits (pipes), comprising steps of:
(a) refilling DI water in etching liquid tank and flushing the conduits with DI water;
(b) refilling etching liquid in etching liquid tank and flushing the conduits with etching liquid (i.e. to flush DI water residue in the conduits away); and
(c) refilling etching liquid in etching liquid tank again.
The PM frequency depends on how often the etching process is conducted; generally, one time a week. It takes about 6 hours for the maintenance crew to run through the whole procedures of FIG. 2. Thus, the conventional PM method is not only time-consuming but also labor-exhausted. Moreover, if large quantities of wafers need to be etched, it is a critical step to clean and maintain the intensively operated etching tool during wafer etching, for the purpose of reducing the particle contamination. The time-consuming conventional PM method, however, is going to prolong the etching process, thus increasing the time cost and production cost.
It is therefore an object of the invention to provide a method of cleaning and maintenance used for a rotational etching tool. By combining the physical characteristics of water (splashed off after striking the surface of a spinning wafer) and a PM (preventive maintenance) computer program, the method can be automatically and quickly applied to do the cleaning job.
The invention achieves the first object by providing a method of cleaning and maintenance used for a rotational etching tool, particularly used for cleaning inner wall of a single process chamber. The rotational etching tool comprises a wafer supporting means and at least two process chambers, the wafer supporting means is moveable between the process chambers, at least a nozzle is positioned above the wafer supporting means for ejecting a cleaning liquid. The method comprises steps of:
(a) floating a wafer over the wafer supporting means, and moving the wafer supporting means to a position associated with one of the process chambers;
(b) applying the cleaning liquid to the wafer;
(c) spinning the wafer supporting means at the first rotating speed for the first duration;
(d) changing the rotation speed of the wafer supporting means to the third rotating speed for the third duration; and
(e) repeating steps of (c) and (d).
The invention achieves the second object by providing another method of cleaning and maintenance used for a rotational etching tool, particularly used for cleaning the sidewalls of the process chambers. The rotational etching tool comprises a wafer supporting means and at least two process chambers, the wafer supporting means is moveable between the process chambers, at least a nozzle is positioned above the wafer supporting means for ejecting a cleaning liquid. The method comprises steps of:
(a) floating a wafer over the wafer supporting means, and moving the wafer supporting means to a position associated with one of the process chambers;
(b) applying the cleaning liquid to the wafer;
(c) spinning the wafer supporting means at the first rotating speed for the first duration;
(d) moving the wafer supporting means to another position associated with another process chamber, and then changing the rotation speed of the wafer supporting means to the second rotating speed and rotating for the second duration; and
(e) repeating steps of (c) and (d).
The invention achieves the third object by combining the two methods described above to clean each process chamber and the sidewall thereof.
The process chambers could be a cleaning chamber, and one or several etching chambers. The cleaning liquid could be deionized (DI) water. The etching liquid could be any liquid generally used in the etching process; for example, a buffered mixture comprising ammonium fluoride and hydrofluoric acid.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.